In 1985, ice cores extracted from Greenland revealed temperatures and CO2 levels going back 150,000 years. Temperature and CO2 seemed locked together. It was a turning point—the “greenhouse effect” captured attention. But, in 1999 it became clear that carbon dioxide rose and fell after temperatures did. By 2003, we had better data showing the lag was 800 ± 200 years. CO2 was in the back seat.

AGW replies: There is roughly an 800-year lag. But even if CO2 doesn’t start the warming trend, it amplifies it.

Skeptics say: If CO2 was a major driver, temperatures would rise indefinitely in a runaway greenhouse effect. This hasn’t happened in 500 million years, so either a mystery factor stops the runaway greenhouse effect, or CO2 is a minor force, and the models are missing the dominant driver.

Amplification is speculation. It’s a theory with no evidence that it matters in the real world.

Conclusion: 1. Ice cores don’t prove what caused past warming or cooling. The simplest explanation is that when temperatures rise, more carbon dioxide enters the atmosphere (because as oceans warm they release more [...]